Investigations into a Perforated Reference Electrode Applied in Small Li-Ion Pouch Cells

Abstract

The use of reference electrodes (REs) in lithium-ion batteries allows enhanced electrochemical analysis of individual electrodes via potential monitoring or electrochemical impedance spectroscopy (EIS). The design and material choice of REs is still under debate. An ideal RE should cover a large proportion of the electrode area in order to measure representative potentials, but also not block the pathway of the lithium ions significantly to avoid distorted measurements. Here, we show studies on an own-designed perforated RE (PRE) based on LiFePO4 applied in ≈60 mAh graphite/NMC811 pouch cells.[1] In our setup shown below, more than 17% of the electrode area is covered and therefore monitored by the PRE, which is a more than fourfold increase compared to our previous work.[2] Despite this large cover proportion, only negligible capacity differences were observed for charge rates up to 2C compared to cells without PRE. At higher rates, the blocking effect caused by the PRE was still very low (7.3% reduced capacity compared to cells without PRE at 5C). Reproducible and plausible anode voltage curves were obtained for all C-rates and the beginning of Li plating at 3C was correctly detected (visually verified by cell teardown). Comparison tests showed that the PRE presence did not have significat influence on the cell EIS spectra. Except for one anode spectrum recorded at a state of charge of 0, the impedance spectra of the individual electrodes recorded by the PRE were confirmative and artifact-free. The results demonstrate that our PRE can be reliably applied for detailed electrochemical investigations of lab-scale electrode coatings in small pouch cell formats.[1] P. Stehle, D. Rutz, A. M. Bazzoun, C. Seidl, I. Bauer, M. Anjass, Energy Technol. 2023, 2300278, DOI: 10.1002/ente.202300278.[2] D. Rutz, F. Brauchle, P. Stehle, I. Bauer, T. Jacob, ChemElectroChem 2023, e202300216, DOI: 10.1002/celc.202300216. Figure 1